1. Field of the Invention
This invention relates to new and useful improvements in drill bits and more particularly to drill bits having improved diamond cutting elements and to the improved cutting elements, per se.
2. Brief Description of the Prior Art
Rotary drill bits used in earth drilling are primarily of two major types. One major type of drill bit is the roller cone bit having three legs depending from a bit body which support three roller cones carrying tungsten carbide teeth for cutting rock and other earth formations. Another major type of rotary drill bit is the diamond bit which has fixed teeth of industrial diamonds supported on the drill body or on metallic or carbide studs or slugs anchored in the drill body.
There are several types of diamond bits known to the drilling industry. In one type, the diamonds are a very small size and randomly distributed in a supporting matrix. Another type contains diamonds of a larger size positioned on the surface of a drill shank in a predetermined pattern. Still another type involves the use of a cutter formed of a polycrystalline diamond supported on a sintered carbide support.
Some of the most recent publications or patents dealing with diamond bits of advanced design, relevant to this invention are Rowley, et al. U.S. Pat. No. 4,073,354 and Rohde, et al. U.S. Pat. No. 4,098,363. An example of cutting inserts using polycrystalline diamond cutters and an illustration of a drill bit using such cutters, is found in Daniels, et al. U.S. Pat. No. 4,156,329.
The most comprehensive treatment of this subject in the literature is probably the chapter entitled STRATAPAX bits, pages 541-591 in ADVANCED DRILLING TECHNIQUES, by William C. Maurer, The Petroleum Publishing Company, 1421 South Sheridan Road, P. O. Box 1260, Tulsa, Okla. 74101, published in 1980. This reference illustrates and discusses in detail the development of the STRATAPAX diamond cutting elements by General Electric and gives several examples of commercial drill bits and prototypes using such cutting elements.
Commercially available diamond cutters consist of disc shaped polycrystalline diamond brazed on a cylindrical stud of tungsten carbide. There are two types generally in use. One is a relatively large diameter cutting disc which is used in soft and medium formations and to some extent in hard formations. Another type has a relatively small diameter cutting disc which is used in hard and very hard formations. The disadvantage of the small cutters is that they are secured to the supporting carbide stud on a relatively small surface area with the result that these cutters undergo much higher shear forces when cutting hard formations. In addition, the small cutters are not very effective when used in softer formations.
These patents and the cited literature show the construction of various diamond bits and related prior art but do not consider the problem of providing adequate bonding of small cutting elements to their supporting studs.